1. Field of the Invention
This invention relates to a method of positioning a work piece and a system therefor, and more particularly to a method of positioning a work piece when a columnar work piece such as a semiconductor ingot is cut into a multitude of thin sheet-shaped wafers by a running wire saw, and a system therefor.
2. Description of the Related Art
One of devices for cutting a work piece such as a columnar semiconductor ingot is a wire saw. In this wire saw, wires are guided around a plurality of grooved rollers to form wire rows, and ends on one side of the wires are wound around one of wire reels and ends on the other side are wound around the other wire reels. Then, when the wires reciprocally run between one of the wire reels and the other at a high speed, the work piece is vertically moved and pressed against the horizontal wire rows, and a working solution containing abrasive grains is supplied to the wire rows, so that the work piece can be cut into a multitude of thin sheet-shaped wafers by lapping action of the abrasive grains.
Then, when the semiconductor ingot (hereinafter referred to as a "work piece") formed of a single crystal material for example is cut by the wire saw, it is necessary to cut the work piece after the work piece is positioned in such a manner that a cut surface of the work piece is set at a predetermined angle, such for example as a crystal orientation.
As a method of positioning the work piece for arranging the crystal orientation, there has heretofore been disclosed one Japanese Patent Application Laid-open No.3-10760. According to this method, individual wire saws are each provided with a gonio angle measuring meter and a gonio angle setting device, whereby the inclination of a push-up base for supporting the work piece is adjusted by the gonio angle setting device on the basis of the result of the crystal orientation of the work piece which has been measured directly in a state where the gonio angle measuring meter is mounted. There is another method, in which a measuring device provided with the gonio angle measuring meter and the gonio angle setting device is provided in addition to the wire saws each of which is provided with the gonio angle measuring meter and the gonio angle setting device, and the gonio angle setting device of this measuring device is connected on line to the gonio angle setting devices of the wire saws, whereby the operating conditions of the gonio angle setting device, which are obtained by this measuring device, are outputted to the gonio angle setting devices of the wire saws.
Furthermore, as another method, there is one, in which the reference of the work piece is matched with the reference of the wire saw and the like by an optical system (microscope), and thereafter, the work piece is inclined by a predetermined angle on the basis of the information on the crystal orientation, which has been previously measured.
However, the method disclosed in Japanese Patent Application Laid-open No.3-10760 presents a disadvantage in that the costs of the system are increased because the gonio angle measuring meters are mounted on the respective wire saws. Furthermore, according to the method, in which the measuring device provided with the gonio angle setting device is provided in addition to the wire saws, the measuring device should be provided with the gonio angle setting device, so that the costs of the system are increased. On the other hand, according to the method of using the optical system, it takes much time for matching the reference of the work piece with the reference of the wire saw and the like, thus presenting the disadvantage in that the working efficiency deteriorates.
In view of these problems, a necessity has been voiced for an inexpensive system, in which the work piece can be easily and quickly positioned at a predetermined reference angle, e.g., a crystal orientation of the work piece at the time of cutting the work piece.
Furthermore, such a problem at the time of cutting the work piece at a predetermined reference angle is presented that, even if the work piece is positioned at the predetermined reference angle, when a worker has incorrectly stretched a wire on a roller by one groove (1 pitch: about 0.5 mm), or when the position of a groove on the grooved roller is shifted, there may be a case where the work piece is cut in such a manner that the angle of the work piece is shifted in the horizontal direction by a shift value.